PRESERVING OLDER TECHNOLOGY BRETT M. JOHNSON TOTAL EARTH SOLUTIONS +61 409 741 127 BJOHNSON@TOTALEARTHSOLUTIONS.COM

1. The GT-1A Mobile Gravimeter
Andrew Gabell, Daniel Olson and Helen Tuckett
Canadian Micro Gravity Pty Ltd

2. GT-1A – Developed by
JSC STC Gravimetric Technology

3. GT-1A – Summary
• GPS-INS gravimeter
• “Dual purpose technology” developed in
the Russian Federation
• GT-1A s/n 1 has collected more than 30,000
line km of data outside of Russia
• GT-1A s/n 2 approaching 10,000 line km
• Installations in a range of vehicles

4. 1. Inertial acceleration (aircraft motion)
1 kg
1 Newton 1 m/sec
2
“. . . they are
identical and
cannot be
distinguished”
A. Einstein
2. Gravitational acceleration (anomalies)
1 kg
~ 9.8 m/sec
2
GT-1A – The Technology
Measuring gravity from a moving vehicle

5. Measuring gravity from a moving vehicle
2. GPS measures:1. Accelerometer measures:
Gravitational
acceleration
(anomaly)
Inertial
Acceleration
(aircraft
motion)
INS platform and
accelerometer
Vehicle floor
Inertial accelerationInertial acceleration
+
Gravitational acceleration (anomaly)
GT-1A – The Technology
GPS receiver

6. GT-1A – Installations

7. The GT-1A – Description
Installation in Cessna 404
Electronics Bay
Gravimeter
UPS
Turntable
Shock Mount
GPS Receiver

8. GT-1A – Vital statistics
• Gravimeter + Turntable + Shock Mount
– 924mm high
– 600mm diameter base plate
– Weight 110kg
– Power consumption 150W
• UPS – 15kg
• CDU – Rugged PC
• GPS receiver

9. GT-1A – Platform

10. GT-1A – Platform
• Housed in double-loop constant-
temperature environment:
– Gravity Sensing Element (GSE)
– Dynamically Tuned Gyro (DTG)
– Fibre Optic Gyro (FOG)
– X and Y accelerometers
– Gravimeter Calibration Devices
(GCDs)

11. GT-1A – Description
Electronics Bay

12. GT-1A – Electronics Bay
• Microprocessor
– Platform measurements @ 300Hz
– GPS feed @ 2Hz
– Main control loop @ 18.75Hz
– Data output @ 18.75 or 3.175 Hz

13. GT-1A – Operating Software
• Runs on CDU
– Pre-flight reference
– In-flight data acquisition
– No operator on board - LED indicates status
during flight
– Post-flight reference
• Automated calibration using GCDs – 5.25 hr

14. GT-1A – Performance
Dynamic Range
• Fine channel +/- 250Gal
• Coarse channel +/- 500Gal

15. GT-1A – Performance
Resolution
• Full wavelength res. = filter length (sec) x velocity (m/sec)

16. GT-1A – Sensitivity
Repeat Lines – s/n1
• 5 repeat lines – GT-1A s/n1 – March 2004 – 107 sec filter
• Noise estimate (Green & Lane method) 0.53mGal (all data)

17. GT-1A – Sensitivity
Repeat Lines – s/n2
• 5 repeat lines – GT-1A s/n2 – May 2004 – 107 sec filter
• Noise estimate (Green & Lane method) 0.47mGal (all data)
• Noise estimate with 80 sec filter 0.38mGal

18. GT-1A – Sensitivity – Repeat Lines

19. • Average of SN1 – Average of SN2 repeat lines
• Standard deviation = 0.29mGal
GT-1A Sensitivity – Repeat Lines

20. • Kalgoorlie Grids – Upward continued ground data on left,
airborne data on right. Std dev of difference grid is 0.43 mGal
GT-1A Sensitivity
Comparison to ground data

21. GT-1A – Data post-processing

22. GT-1A – Summary
• Small, light, low power consumption
• Simple logistics (no operator)
• Dual dynamic ranges - +/-250 & +/- 500Gals
• Sensitivity 0.6mGal with 100 sec filter
• Resolution (half-wavelength) of 2.0 to 3.5km
@ speeds of 50 to 70m/sec
• High productivity – short lead-ins/outs
• Installations in a range of vehicles

23. Vredefort Dome S.Africa
• Aircraft Cessna 208 Caravan
• Height: 450 m AGL constant height
• Area 64 x 98 kms 2 km line spacing
• Courtesy of FAS Central Region and the Council for Geoscience for SA